Adidas says it took 18 months to perfect the fitness smartwatch. Designers started with a clunky contraption that included a stride sensor, heart-rate strap, and wired headphones, but found that runners really wanted GPS, music, and accurate coaching without needing to carry a phone or tangle of cords. By providing those features through a Bluetooth connection to a wireless headset, Gaudio says, he believes the miCoach Smart Run has "all the key elements that any runner needs."

By fitting the silicone strap with LEDs that shine through the skin, the sensor detects the reflections, and then pairs that data with the built-in accelerometer to run an algorithm that calculates accurate heart-rate data. "The special sauce behind it is the data sensor itself," Gaudio says. "It was the key enabler for us. Once we had access to that, we had what we wanted to make a killer app."

The 1.45-inch thin-film, color LCD touchscreen offers more than 400 animations of workouts and plans and color-coded workouts customized to the user's desired goals and abilities (partially determined by heart rate data). The system can coach via audio and visual cues or watch vibration. Everything syncs with a web platform, but the 4GB of memory on the watch allows for saved workouts and music.

"The whole object with miCoach is to take the science in elite-level training and make it simple," Gaudio says. "Heart-rate training is the best way to train the body, so we take the guesswork out of it."

Tim Newcomb covers infrastructure and sports for Popular Mechanics. Follow him on Twitter at @tdnewcomb.